The present invention relates to instruments for obtaining tissue samples, particularly for mammary biopsy procedures. More particularly, the invention relates to improved instruments for mechanically powered needle assemblies to sample the diagnostic tissue.
Syringe-type sampling instruments referred to as so-called Menghini needles incorporate an outer cylindrical body which is connected at one end to a hollow cannula needle through which a needle stylet is slidably supported on a piston inside the cylindrical body, as more fully described in U.S. Pat. No. 4,619,272. This patent describes operation of the piston and cylinder to create a suction chamber which draws tissue sample into the connected cylindrical cannula. The instrument described in this patent, however, requires manual operation of the piston.
Additional development of such syringe-type biopsy needle instruments is described U.S. Pat. No. 5,172,701. This patent describes a spring-driven piston in which the cylinder is formed by the housing itself so that the suction chamber is dependent on the housing dimension. This patent also describes instruments in which the spring is located within the suction chamber with consequent reduction in the volumetric ratio of the chamber expansion and suction action which can be developed for aspirating tissue sample into the cannula. These instruments also incorporate a complex one-way valve for venting the suction chamber.
These and other disadvantages are eliminated in improved tissue sampling instruments according to the present invention.